Faceted LED street lamp lens

ABSTRACT

A lens for an LED street lamp has an external curved surface that has a concave surface portion on one side thereof. A back surface of the lens has a micro-prism array and retainer feet. A recess in the back surface receives an LED light source. The outer surface of the lens has facets or windows that provide overlapping projections of light from adjacent facets. The lens is generally cushion shaped with an indentation at one side. The lens directs light in an asymmetrical distribution transverse to the lens and to direct light symmetrically over a wide area in a longitudinal direction of the lens.

FIELD OF THE INVENTION

The present invention relates generally to a lens for use in a streetlamp, and more particularly to a lens for use with a light emittingdiode (“LED”) street lamp.

BACKGROUND OF THE INVENTION

LEDs are energy-efficient and environmentally friendly and feature highlighting efficiency and long working life. As such, LEDs have seen moreextensive applications lighting installations in general andspecifically in road illumination as a new generation of green,energy-efficient light sources. LED street lamps have become a leadingchoice in the transformation of road lighting for energy conservation.However, from the perspective of illumination. LED street lamps stillface technical problems in four areas, namely lighting efficiency, lightdistribution, light attenuation and color temperature. Considerableimprovements have been made in the lighting efficiency, lightdistribution, and light attenuation of LED street lamps due to rapiddevelopments in LED semiconductor techniques, secondary lightdistribution technology, and heat-radiating technology.

For example, the various secondary optical lens types such as thosehaving a free-curved-face peanut shape, a saddle shape or an asymmetriccurved face for polarization can distribute light emitted by LED intohighly-efficient uniform light patches of a rectangular shape. Thecurved surface for light distribution adopts a bat-wing shape is welladapted to satisfying the design standards of urban road illumination inChina.

However, until now there has been no satisfactory solution to the colortemperature differences (i.e., color differences) of LED street lamps.The uneven application of fluorescent powders on the light-emittingsurface of LED chips and the color differences inherent to the secondaryoptical lens will normally generate different color temperatures in themiddle and at the edges of the projected light patches. The lightpatches are bluish with a higher color temperature in the middle, butyellowish with a lower color temperature at the edges. In addition,color temperature is an important parameter affecting the performance ofLED street lamps, and its spatial distribution is highly significant forproduct performance.

The relevant color temperature refers to the temperature of a black-bodyradiator that is most similar to the color of the same brightnessstimulus. The relevant color temperature difference distinguishable bythe human eye may be as low as 50-100K, compared to up to severalhundred K in the differences in the spatial distribution of relevantcolor temperatures of LED street lamps. The lens with color differenceswill generate highly distinctive yellow-and-white “optical zebracrossings” on the road surface, and hence severely affect the visualeffect of the street lamp.

BRIEF SUMMARY OF THE INVENTION

In consideration of the above, a first aspect of the present inventionprovides a secondary optical lens of an LED street lamp which integratesan optical lens featuring a free curved surface for oblique lightdistribution with faceted face technology that provides a light-mixingeffect. The street lamp lens distributes the light rays emitted by theLED over a wide-angle along the X-X or longitudinal section of the lens(along the road direction) and over an asymmetrical and oblique anglealong the Y-Y or lateral section of the lens (perpendicular to the roaddirection). The curved surface of the lens that provides lightdistribution of the lens has many miniature facets thereon that providea light-mixing function. All light rays that are outputted from eachminiature facet have a very small dispersion angle of their own, andthey form light patches of uniform color temperature as a result ofoverlapping of the light patches emitted by nearby facets. Thisconfiguration fully solves the color difference problems of LED streetlamp light patches, i.e., bluish in the middle and yellowish at theedges of the light patches, eliminates the “optical zebra crossing” onthe road surface, and hence ensures the uniform distribution of lightpatches on the road surface.

Since secondary optical lens according to this first aspect of thepresent invention has a light-mixing effect, the LED adopted for thislens may include a single-chip LED, a multi-chip LED, a COB (chip onboard) module LED light source. The COB module is a device in which thechip arrays are integrated on the same printed circuit board to form alight source module. The light patches will not project the shadow ofthe LED's multi-chip array.

In a second aspect of the present invention, a lens for an LED streetlamp for use with an LED light source having a primary lens, comprisinga leas body of a secondary optical lens, the lens body having a curvedouter surface, from which light is emitted, the curved outer surfacehaving a first perimeter portion and a second perimeter portion oppositethe first perimeter portion; a back surface opposite the curved outersurface, the back surface defining a recess for receiving the LED lightsource, the recess being closer to the first perimeter portion than tothe second perimeter portion; a reflective micro-prism array formed onthe back surface; the curved outer surface defining a concave surfaceportion at the first perimeter portion; a plurality of facets on thecurved outer surface; and a mounting structure for mounting the lensbody.

In another aspect of the present invention, the lens body has alongitudinal axis and a transverse axis, the lens body being shaped toprovide optical characteristics to emit light from the LED light sourceover a wide distribution angle at a cross section along the longitudinalaxis and to emit light from the LED light source over an obliquedistribution angle at a cross section along the transverse axis.

In another aspect of the present invention, each of the facets on thecurved outer surface of the lens body is configured to output light overa narrow angle, the facets being arranged to emit light patches thatoverlap light emitted from other facets to provide light mixing so thata substantially uniform color temperature light is output from thesecondary lens.

In another aspect of the present invention, the curved outer surface ofthe lens body is shaped to emit light at an axis of refraction that isdisposed at an angle relative to an optical axis of the light source ofbetween 30 degrees and 70 degrees inclusive at a cross section of thelens body along the transverse axis.

In another aspect of the present invention, the recess includes asurface facing the LED light source that is configured to collect lightrays emitted by the LED light source and refract the light rays towardthe external curved surface for light distribution.

In another aspect of the present invention, the reflective micro-prismarray on the back surface is configured to collect light reflectedinternally by the curved outer surface and to reflect the collectedlight toward the curved outer surface to distribution by the lens body.

In another aspect of the present invention, the mounting structureincludes a plurality of retainer feet extending from the back surface ofthe lens body, the retainer feet being non-optical elements.

In another aspect of the present invention, the lens body is configuredfor use with at least one of the LED light sources selected from thegroup consisting of: a single chip LED light source, a multi-chip LEDlight source, and a chip-on-board module LED light source.

In another aspect of the present invention, the lens body is shaped torefract light from a center of the light source so that light emittedfrom the lens body is emitted with an axis of refraction that isdisposed at an angle of between 30 degrees and 70 degrees inclusive froman optical axis of the LED light source at a cross section along thetransverse axis of the lens body, the lens body being shaped to refractlight from a center of the light source so that a marginal emitted lightray is disposed at an angle of −20 degrees to −45 degrees inclusiverelative to the optical axis of the light source at a cross sectionalong the transverse axis of the lens.

In another aspect of the present invention, the lens body is shaped torefract a single ray of light emitted from a center of the light sourceat an angle θ1 relative to the optical axis of the light source so thatthe ray of light is emitted from the curved outer surface at an angle ofθ2 relative to the optical axis of the light source, wherein θ1 and θ2satisfy the equation

${{\theta\; 2} = {\tan^{- 1}\left\{ {{\left( \frac{{90{^\circ}} - {\theta\; 1}}{{90{^\circ}} + \delta} \right)\left\lbrack {{\tan(\delta)} - {\tan(\alpha)}} \right\rbrack} + {\tan(\alpha)}} \right\}}},$wherein δ is an angle of an axis of retraction relative to the opticalaxis of the light source and α is an angle of a marginal light myrelative to the optical axis of the light source, at a cross sectionalong the transverse axis of the lens.

In another aspect of the present invention, the lens body is shaped torefract light from a center of the light source so that the lightemitted from the lens body is distributed in an emission angle ofbetween 120 degrees to 155 degrees inclusive at a cross section alongthe longitudinal axis of the lens.

In another aspect of the present invention, the lens body is shaped torefract a single ray of light emitted from a center of the light sourceat an angle ξ1 relative to an optical axis of the light source so thatthe ray of light is emitted from the curved outer surface at an angle ξ2relative the optical axis of the light source, wherein ξ1 and ξ2 satisfythe equation

${{\xi\; 2} = {\tan^{- 1}\left\lbrack {\frac{\xi\; 1}{90{^\circ}} \cdot {\tan(\psi)}} \right\rbrack}},$wherein Ψ is an angle of distribution of light from the lens body, at across section along the longitudinal axis of the lens.

In another aspect of the present invention, the facets include at leastone of a flat plane, a concave face, and a convex face, the facets beingarranged to emit light patches that overlap light emitted from otherfacets to provide light mixing so that a substantially uniform colortemperature light is output from the secondary lens.

In another aspect of the present invention, the surface of a facet onthe curved outer surface and a projection of the facet on the innersurface of the recess with reference to a center of the light sourceform a false lens having a divergent effect on light emitted from thefacet, wherein light emitted from a center of the light source throughthe facet is spread by a divergent angle of approximately 3 degrees to 5degrees inclusive, along a cross section taken along a transverse axisof the lens.

In another aspect of the present invention, the surface of a facet onthe curved outer surface and a projection of the facet on the innersurface of the recess with reference to a center of the light sourceform a false lens having a divergent effect op light emitted from thefacet, wherein light emitted from a center of the light source throughthe facet is spread by a divergent angle of approximately 3 degrees to 5degrees inclusive, along a cross section taken along a longitudinal axisof the lens.

In another aspect of the present invention, the micro-prism array on theback surface of the lens body includes one of a pyramid reflectorstructure, a cube-corner reflector structure, and a conical reflectorstructure.

In a further aspect of the present invention, a method is provided fordirecting light from an LED light source onto a surface, including:directing light from the LED light source in an emission pattern in aprimary emission direction, wherein the emission pattern is elongated ina direction transverse to a direction of emission; mixing refractedcolors of light from the LED light source to provide a mixed color lightemission in the primary emission direction; and redirecting light fromthe LED light source that is reflected from the primary emissiondirection so that the reflected light is returned to the primaryemission direction.

In yet another aspect of the present invention, a method is provided fordirecting light from an LED light source onto a surface, the lightsource defining a parallel plane that is parallel to a light emittingsurface of the LED light source, including: enclosing a light emittingportion of the LED light source with a first refracting surface of anoptical body; disposing the first refracting surface at a substantiallyconstant distance from the LED light source in a first perpendicularplane; disposing the first refracting surface at a varying distance fromthe LED light source in a second perpendicular plane, the first andsecond perpendicular planes being perpendicular to one another andperpendicular to the parallel plane of the LED light source; directinglight from the LED light source into the first refracting surface of theoptical body; emitting the light from the LED light source from a secondrefracting surface of the optical body, the emitted light defining arefracting axis offset by an angle from the first perpendicular plane,the refracting axis of the emitted light being disposed in the secondperpendicular plane, the emitted light having a greatest intensity atthe refracting axis; the emitting the tight including emitting the lightfrom the LED light source in a emission pattern having a greater extentalong an axis parallel to the first perpendicular plane and a lesserextent along an axis in the second perpendicular plane; mixing refractedcolors of the emitted light by directing the emitted light through aplurality of facet surfaces at the second refracting surface; reflectinga portion of the light from the LED light source at the secondrefracting surface to generate first reflected light; and reflecting thefirst reflected light at a reflecting surface to provide a secondreflected light, the second reflected light being directed toward thesecond retracting surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures are for illustration purposes only and are not necessarilydrawn to scale. The invention itself, however, may best be understood byreference to the detailed description which follows when taking inconjunction with the accompanying drawings in which:

FIG. 1 is a front view of an LED street lamp lens according to theprinciples of the present invention;

FIG. 2 is an isometric view of the street lamp lens of FIG. 1;

FIG. 3 is a top plan view of the street lamp lens;

FIG. 4 is a side view of the street lamp lens;

FIG. 5 is a bottom plan view of the street lamp lens;

FIG. 6 is a cross-sectional view of the street lamp lens along line X-Xof FIG. 3;

FIG. 7 is a cross-sectional view of the street lamp lens along line Y-Yof FIG. 3;

FIG. 8 is a schematic representation of light distribution from thestreet lamp lens;

FIG. 9 is a schematic diagram of a single ray of light emitted by thestreet lamp lens;

FIG. 10 is schematic diagram of light distribution along an X axis ofthe street lamp lens;

FIG. 11 is a schematic diagram of a single ray of light emitted from thestreet lamp lens along an X axis;

FIG. 12 is a schematic diagram of adjacent rays of light being emittedfrom the street lamp lens along the Y axis;

FIG. 13 is a schematic diagram of adjacent rays of light being emittedfrom the street lamp lens along the X axis;

FIG. 14 is a schematic diagram of a single ray of light being emittedfrom the street lamp lens that includes a micro-prism back plane;

FIG. 15 is a side view of a 3D model of the street lamp lens;

FIG. 16 is a front perspective view of the 3D model of the street lamplens;

FIG. 17 is a back perspective view of the 3D model of the street lamplens;

FIG. 18 is a ray tracing diagram front an end view of the street lamplens;

FIG. 19 is a ray tracing diagram from a side view of the street lamplens;

FIG. 20 is a graph of contour lines of light output from the street lamplens;

FIG. 21 is a side view of the contour lines of light output along the Yaxis of FIG. 20;

FIG. 22 is a side view of the contour lines of light output along the Xaxis of FIG. 20;

FIG. 23 is a graph of light distribution emitted by the street tamplens; and

FIG. 24 is an illustration of illumination on a three-lane road surfaceby street lamps using the street lamp lens.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, a front view of a lens element 10 for a street lamp is shown.The lens 10 has a domed outer surface 12 that is elongated in a middleportion 15 that is shaped with a large radius curve. Ends 16 of thedomed surface 12 are curved more sharply with a smaller radius curve.The domed surface 12 extends downwardly (with respect to the drawingfigure) to a perimeter band 17 that extends about the outer perimeter ofthe lens 10. The domed surface 12 is shaped with facets or small windows18 in a pattern over the domed surface 10. The perimeter 17 likewise hasfacets or small windows 19.

A back surface 13 opposite the domed surface 12 is provided withmicro-prisms 20. Three legs 14 extend from the back surface 13.

FIG. 2 shows the lens 10 of a generally cushion shape with anarrangement of generally rectangular facets or windows 18 on the domedouter surface 12. The perimeter band 17 includes generally rectangularshaped facets or windows 19. Triangular facets or windows 22 arearranged at the interface between the perimeter band 17 and the domedsurface 12 in a transition zone. The transition zone also includestrapezoidal shaped facets or windows 24.

With reference to FIG. 3, the lens 10 is symmetrical about a Y axis andasymmetrical about an X axis. The X axis, indicated by the line X-X, isoffset from the center line of the lens 10. The X axis separates alarger portion 26 from a smaller portion 28. The perimeter of the largerportion 26 is convex in shape, whereas the perimeter of the smallerportion 28 includes end portions that are convex and a center portion 30that is of a concave shape. In other words, the perimeter is slightlyindented, or concave, at the center 30 of the smaller portion 28.

In the end view of FIG. 4, the lens 10 has the legs 14 offset toward thelarger portion 26. In particular, a leg 14 a is disposed near theperimeter 17 of the larger portion 26. A leg 14 b is disposed at or nearthe X axis of the lens 10. No leg is at the perimeter of the smallerportion 28.

FIG. 5 shows a view of the back surface 13. The back surface 13 iscovered in the micro-prisms 20 except for a center portion 32 thatincludes a concave recess 11. The center portion 12 is rectangular inshape. The recess 11 is of an oval or egg shape. Three legs 14 arelocated in the micro-prism portion 20 and are circular in plan view. Oneof the legs 14 a is disposed on the Y axis between the long axis of therecess 11 and the perimeter 17. The other two legs 14 b are on the Xaxis between the recess 11 and the perimeter 17 along the short axis ofthe oval recess 11. The legs 14 are provided for mounting and/orretaining the lens 10 in position when the lens 10 is assembled in astreet light fixture for use. The legs 14 may be of any shape requiredfor mounting the lens.

With reference to FIG. 6, the lens 10 is shown in cross section alongthe X axis. The cross sectional view extends through the legs 14 b andthrough the micro-prisms 20 on the back surface 13. The micro-prisms 20of a preferred embodiment are provided with a reflective coating,although they may be uncoated in other embodiments. The recess 11 has agenerally semi-circular shape in this cross section. A multi-chip LEDlight source 34 is mounted at the recess 11. The light source 24includes a base 36 on which electrical components may be mountedincluding one or more LED elements 38. A lens 40 is mounted on the base36 of the light source. The lens 40 extends to adjacent the surface ofthe recess 11. The lens 40 on the LED light source 34 may be referred toas a primary lens and the lens 10 may be referred to as a secondaryoptical lens.

The LED light source used with the present lens may include single-chipLED, a multi-chip LED, or a COB (chip on board) module LED light source.Other light sources are, of course, possible. The lens 10 is structuredso that the emitted light patches will not project the shadow of theLED's of a multi-chip array if a multi-chip array is used.

In FIG. 7, the secondary lens 10 includes the domed outer surface 12offset relative to the X axis and offset relative to the recess 11 inthis cross-sectional view taken along the Y axis. The leg 14 extendsfrom the micro-prism formed back surface 13 to one side of the recess11. The LED light source 34 is positioned within the recess 11 with thebase 36 and primary lens 40 generally along the X axis of the secondarylens 10. The primary lens 40 is semicircular in shaped in this sectionalview, but the recess 11 is elongated in the Y direction of the secondarylens 10. This results in a gap 42 between the primary lens 40 and thesecondary lens 30. The gap 42 is narrowest at the peak of the primarylens and increases to either side. The gap is asymmetrical and is largertoward the larger portion 26 of the secondary lens 10 than toward thesmaller portion 28. The asymmetrical shape of the secondary lens 10results in the body of the lens 10 being thicker at the larger portion26 and thinner at the smaller portion 28.

Turning to FIG. 8, a light distribution pattern 44 is shown in a crosssection along the Y-Y axis. The light source 34 includes multiple LEDlight sources that project light from the base 36 through the primarylens 40. The primary lens 40 may be hemispherical or parabolic or othershape. In one example, the primary lens is rotationally symmetrical.Light, indicated by radial lines extending from the light source 34, isdistributed over a wide angle of approximately 180 degrees by theprimary lens 40, although it is likely that them is a predominance oflight emitted at the optical axis of the light source due the nature ofLEDs.

Light leaving the light source 34 encounters the inner surface of therecess 11 and enters the secondary lens 10. A combination of refractionand the shaping of the secondary lens 10 results in the light emittedfrom the secondary lens having an asymmetrical distribution. Inparticular, the emitted light is directed along a primary direction Tthat is at an angle δ from a perpendicular direction Z from the base 36at O. The refracting angles of light beams emitted by the lens 10 bendtoward the primary direction T, so that the primary direction may bereferred to as the axis of refraction. Stated another way, the axis ofrefraction is at an angle δ to the perpendicular Z of the light source.The light is emitted at the smaller portion of the lens 10, which isnearer the light source 34 as a result of the asymmetric structure ofthe lens 10, is at a maximum refraction angle α.

The principles of light distribution along the Y-Y section on the baseface of the curved outer surface 12 of the secondary optical lensinvolved are as follows. The light ray emitted from point O at thecenter of the light-emitting face of the multi-chip LED light source 34is retracted by the concave incident face of the recess 11 onto the baseface of curved surface 12. The base face of the curved outer surface 12distributes the incident light ray in an oblique manner and the axis ofthe emergent light ray is OT, i.e. all emergent light beams exit alongthe OT axis after light distribution. The angle between the refractingaxis OT of the lens 10 and the optical axis OZ of the light source thatpasses point O at the center of the LED light-emitting face andperpendicular to the chip light-emitting face is δ; δ is between 30degrees and 70 degrees; here δ is preferably selected as 45 degrees. Forthe marginal light ray emitted from point Q at the center of the chiplight-emitting face and crossing the rightmost side of the base face ofcurved surface 12, the angle between the emergent marginal light ray andthe optical axis OZ is α; where α is between −20 degrees and −45degrees, and here α is preferably selected as −35 degrees. Here it isassumed that the angle is positive when the light ray is to the left ofoptical axis OZ, and negative when it is to the right of OZ.

In FIG. 9 a single light ray is emitted from the secondary lens 10. Thesingle light ray explains the distribution of light along the Y axis ofthe lens 10. For the secondary optical lens 10 according to a preferredembodiment, a light ray is distributed by the base face of the curvedouter surface 12 along the Y-Y section. A light ray OB emitted frompoint O at the center of the light-emitting face of the multi-chip LEDlight source 34 is refracted by the concave incident face of the recess11 onto point C on the base face of curved surface 12, and outputted aslight ray CD after light distribution. Assuming that the angle betweenlight ray OS and optical axis OZ of the light source is θ1 and the anglebetween the emergent light ray CD and the optical axis OZ is θ2, both θ2and θ1 shall satisfy the following light distribution conditions:

$\begin{matrix}{{\theta\; 2} = {\tan^{- 1}\left\{ {{\left( \frac{{90{^\circ}} - {\theta\; 1}}{{90{^\circ}} + \delta} \right)\left\lbrack {{\tan(\delta)} - {\tan(\alpha)}} \right\rbrack} + {\tan(\alpha)}} \right\}}} & {{Equation}\mspace{14mu}(1)}\end{matrix}$

The coordinates (X, Y) of each point on the contour line along the Y-Ysection of the base face of curved surface 12 can be calculated usingiteration in the numerical calculation method of the curve according tothe light distribution conditions of emergent and incident light rays asspecified in Equation (1). Thus the shape of the section's contour linecan be determined.

In FIG. 10, the light distribution along the X-X section of thesecondary optical lens 10 provides a different distribution pattern thanthat along the Y-Y axis. The principles of light distribution along theX-X section on the base face of the curved outer surface 12 provide awide, symmetrical distribution. The light rays emitted from point O atthe center of the light-emitting face of the multi-chip LED light source34 are refracted by the concave incident face of the recess 11 onto thebase face of the curved outer surface 12. The base face of the curvedouter surface 12 distributes the incident light rays in a wide-anglespectrum. The angle of emergent light rays has a full width 2Ψ; 2Ψ isbetween 120 degrees and 155 degrees, and here 2Ψ is preferably selectedas 150 degrees.

In FIG. 11 a single light ray along the X-X section of the lens 10 istransmitted from the curved outer surface 12 of the secondary opticallens. The distribution of light along the X-X section is explained withreference to the single light ray. A light ray OP emitted from point Oat the center of the light-emitting face of the multi-chip LED lightsource 34 is refracted by the concave incident face of the recess 11onto point Q on the base face of curved outer surface 12 and outputtedas a light ray QR after light distribution. Assuming that the anglebetween light ray OP and optical axis OZ of the light source is ξ1 andthe angle between the emergent light ray QR and the optical axis OZ isξ2, both ξ2 and ξ1 shall satisfy the following light distributionconditions:

$\begin{matrix}{{\xi\; 2} = {\tan^{- 1}\left\lbrack {\frac{\xi\; 1}{90{^\circ}} \cdot {\tan(\psi)}} \right\rbrack}} & {{Equation}\mspace{14mu}(2)}\end{matrix}$

The coordinates (X, Y) of each point on the contour line along the X-Xsection of the base face of curved surface 12 can be calculated usingiteration in the numerical calculation method of the curve according tothe light-distribution conditions of emergent and incident light rays asspecified in Equation (2). Thus the shape of the section's contour linecan be determined.

The contour lines of the base face of curved surface 12 on the X-X andY-Y sections calculated according to Equations (1) and (2) above arefurther scanned via 3-D modeling software in order to establish a 3-Dsolid model of the lens.

The curved outer surface 12 is assumed to be a smooth curved surface inthe 3-D solid lens model that is constructed according to the lightdistribution Equations (1) and (2). This will result in the projectedlight patches having color differences, i.e. bluish in the middle andyellowish at the edges, due to differences in refraction of thedifferent colors of light by the lens. In the preferred embodiment,light-mixing facets or windows are provided on the curved outer surface12. A so-called light-mixing facet or window may take the form of asmall planar face, a small convex face or a small concave face. Thefacet or window generates a dispersed light beam with a very smalldispersion angle. The dispersed light beams generated by each smallfacet overlap to create a light-mixing effect. The overlapped lightpatches have relatively uniform color temperature. Small planar facetsare preferably selected for light-mixing according to one embodiment.

Referring to FIG. 12, a single facet or window C is show on the curvedouter surface 12 of the secondary optical lens 10 in a schematic diagramalong the Y-Y section showing light-mixing. The light-mixing in thisexample of a single facet occurs for facets over the entire outersurface 12 of the secondary optical lens 10. Assuming that the lightincident on the small facet on the curved surface defines an includedangle established by lines C1-C′-C2 on the outer surface 12. The camberline or bisector line has a radius of curvature of R′. The projection ofthe facet surface on the surface of the recess is established by linesC1-C-C2, which has a local radius of curvature of R. The projection ofthe facet on the outer surface as defined by lines C1-C′-C2 and on theinner surface of the recess as defined by lines C1-C-C2 will form aminiature false lens. The light rays emitted from the point O at thecenter of the LED light-emitting face will generate an angle ofdivergence at a size of ±Δθ here after passing this false lens. Theangle of divergence ±Δθ equals the numerical aperture angle of the falselens formed, and is related to the facet's radius of curvature R′ andthe local radius of curvature R of the base face, or inner surface ofthe recess, of curved surface 12 at this point. For facet dispersionangle Δθ, a range of approximately 3 degrees to approximately 5 degreesis preferably selected. The dispersion caused by the facets cause thelight output by the facets to overlap and thereby provide color mixingof the light from nearby facets.

With reference to FIG. 13, light-mixing dispersion by a single facet oncurved outer surface 12 is shown along the X-X section. The schematicdiagram of light-mixing of a single facet may be translated to multiplefacets on the curved outer surface 12 of the secondary optical lens 10.Assuming that the angle of the incident light on the section of thesmall facet on curved surface 12 is defined by the included angle of thelines Q1-Q′-Q2; that the camber lines line has a radius of curvature ofR′; and that projected incident light is defined by the angle of linesQ1-Q-Q2 on the base face or surface of the recess, and that this innersurface has a local radius of curvature of R, the surfaces defined bythe lines Q1-Q′-Q2 and Q1-Q-Q2 will form a miniature false lens. Thelight rays emitted from point O at the center of the LED light-emittingface will generate an angle of divergence at a size of ±Δξ here afterpassing this false lens. The angle of divergence ±Δξ equals thenumerical aperture angle of the false lens formed, and is related to thefacet's radius of curvature R′ and the local radius of curvature R ofthe base face of curved surface 12 at this point. For Δξ, a range ofapproximately 3 degrees to approximately 5 degrees is preferablyselected.

The diffused light beams generated by numerous facets on the curvedsurface 12 of the lens are overlapped and mixed to form light patches ofuniform color temperature on the road surface, hence essentiallyeliminating the color temperature differences between the middle and theedges of the light patches.

So far, the discussion of light dispersion and overcoming diffractioneffects has focused on the outer surface 12. The back surface 13 wasassumed to be smooth and have no impact on the emitted light. In FIG. 14micro-prisms are provided on the back surface 13 to provide stray lightcollection by the micro-prisms 20 formed in the back of the secondaryoptical lens 10.

When the curved outer surface 12 of the secondary optical lens 10distributes the incident light rays on the X-X section, the emergentlight beams have a very large angle. Therefore, the Fresnel reflectionloss will be very high at the lens medium/air interface. Such Fresnelreflection loss will be reflected by the air interface onto the back 13of the lens 10 in the form of stray light, as shown by the dotted lineQS in FIG. 14. If the back 13 of the lens is not treated in any way,this portion of light energy cannot be used and will be lost. Inconsideration thereof, a micro-prism array 20 with reflective effects isprovided at the back of the lens according to one embodiment. Themicro-prism array 20 may be formed of elements having a pyramid-shaped,a corner cube shaped or a conical shaped structure; a pyramid structureis preferably selected for the micro-prism elements here. The pyramidreflector structure can realize two total reflections of the stray lightQS, re-collect it and cast it towards the front of the lens (as dottedline TU of FIG. 14 shows). Therefore, the outputted light can bedirected onto a road surface (the output light ray UV shown in FIG. 9),hence maximizing the output efficiency of the lens.

FIG. 15 is a 3-D model of the secondary optical lens 10 showing therelative positions of the elements. The light source 34 is locatedoff-center of the lens 10. The faceted outer surface 12 provides eitherplanar, convex or concave surface portions or windows for distributingthe emitted light without separation of colors due to refraction. Thelower surface of the light source 34 is even with the peaks of themicro-prism array 20 of the back surface 13 in this embodiment.

FIG. 16 shows the outer surface 12 including the facets or windows 18 onthe domed surface 12 and the facets 19 on the perimeter 17. FIG. 17shows the back surface 13 with the micro-prism array 20 and the recess11 into which the light source 34 is mounted.

Turning to FIGS. 18 and 19, in one example, an LED light source 34 inthe form of an American CREE MKR four-chip LED with a luminous flux of800 lumens was mounted in a street lamp lens 10 according to anembodiment of the present invention. An observation screen was placed 10meters before the lens. The tracing of the light rays emitted from thefaceted lens 10 is shown in the transverse and longitudinal directionsin FIGS. 18 and 19, respectively. In the transverse view of FIG. 18, thelight rays are asymmetrical with a concentration of light toward thelarger portion of the lens 10. The light rays are distributed evenly inthe longitudinal view of FIG. 19.

FIG. 20 shows the contour lines 46 of illumination intensity on anobservation screen located 10 meters in front of the lens 10. It can beseen that the resulting light patch 48 is distributed in an elongatedoval shape. When mounted above a road surface in a street light fixturewith the long axis of the elongated oval parallel to the road direction,the light patch 48 is over 35 meters in length along the road direction,and about 18 meters wide perpendicular to the road direction. Lightintensity values 50 for the contour lines of FIG. 20 are plotted inFIGS. 21 and 22.

FIG. 23 is a graph of the far-field angle distribution of the lightintensity of the lens, i.e. the curve of light distribution. In the Hdirection, the curve 52 of light distribution takes the shape of awide-angle bat wing, with the light beam angle having a full width ofabout 150 degrees. In the V direction, however, the curve 54 of lightdistribution is off-axis, with the light beam angle having a foil widthof about 80 degrees.

A simulation was run of the LED street lamp lenses mounted along aroadway. For the simulation, an input the IES file of the lens plus CREEMKR light source into the road illumination effect software. Thesimulation assumes that the road is 12 meters wide and has 3 lanes; theroad is a Class R3 road with a maintenance factor of 0.8 and is made ofasphalt; the lamp head is at a height of 10 meters, the lamp post has anoutreach of 1 meter over the road surface and the cantilever is 1.5meters long; the lamp post interval is 35 meters; and the lightingfixture has a luminous flux of 14,900 lumens (140 watts). Then alluniformity parameters of its illumination and brightness (luminance)satisfy all necessary design standards of road lighting, as FIG. 14 andFIG. 15 show.

The simulation results are as follows:

Maintenance factor: 0.80 Scale: 1:294 Grid: 12 × 9 points Appurtenantstreet environment factors: Road 1. Asphalt: R3, q0: 0.070 Selectedillumination class: ME4b (All luminosity requirements have beensatisfied.) Average brightness Surrounding [cd/m²] U0 UI TI [%]illumination factors Calculated actual value: 0.91 0.43 0.85 11 0.51Value set as per class: ≧0.75 ≧0.40 ≧0.50 ≦15 ≧0.50Satisfied/unsatisfied: ✓ ✓ ✓ ✓ ✓ Appurtenant Average observer (3quantities): brightness No. Observer Position [m] [cd/m²] [cd/m²] U0 UITI [%] 1 Observer 1 (−60.000, 2.000, 1.500) 0.91 0.44 0.88 11 2 Observer2 (−60.000, 6.000, 1.500) 0.98 0.43 0.85 10 3 Observer 3 (−60.000,10.000, 1.500) 1.04 0.43 0.92 7

FIG. 24 shows a simulation of a three lane road 56 illuminated accordingto the foregoing example. Contour lines of light intensity 58 areoverlaid on the road 56 for two adjacent street lamps using thesecondary lens 10 according to the present example. The simulation showsthe results of road illumination effects of 140-watt lamps that includethe secondary optical lens of the preferred embodiment. Light isdistributed in elongated areas extending along the direction of theroad. The light output is efficient in that the light output of onelight fixture extends to the light output of a next light fixture, andexcess light is not spilled onto area outside of the roadway. Thesecondary lens 10 provides control of the light output of the streetlight fixtures.

Data for the road illumination simulation include the following.

Grid: 12 × 9 Points [Minimum] [Minimum] Average [Minimum] Maximumillumination/ illumination/ illumination illumination illuminationAverage Maximum [1×] [1×] [1×] illumination illumination 14 7.49 280.529 0.265

Thus, there is shown and described a secondary optical lens featuringlight-mixing effect and uniform color temperature, and used formulti-chip LED light source. The lens consists of the external facetedcurved surface for light distribution, the concave incident faceproximal to the LED side, the reflective micro-prism array face on thebottom, and the retainer feet for assembly purpose.

The secondary optical lens has its external faceted curved surface forlight distribution has the following optical characteristics: Itdistributes the light rays emitted by LED within a wide-angle spectrumalong X-X section (along the road direction) and within an asymmetricaland oblique spectrum along the Y-Y section (perpendicular to the roaddirection).

The secondary optical lens has its external curved surface for lightdistribution including many miniature facets thereon for light-mixing.All light rays outputted from each miniature facet have a very smalldiffusion angle of their own, and they form light patches of uniformcolor temperature after overlapping.

The secondary optical lens of an embodiment has an external curvedsurface for light distribution has an oblique axis along the Y-Ysection. Its angle with the LED optical axis is δ, and δ is between 30degrees and 70 degrees.

The secondary optical lens preferably has its concave incident faceproximal to the LED side works to collect the light rays emitted by theLED and refract them onto the external curved surface for lightdistribution.

The secondary optical lens may include the reflective micro-prism arrayface on the back surface to collect stray light scattered from theexternal curved surface for light distribution and output the lightthrough the curved surface for light distribution, hence increasing theefficiency of the lens.

The secondary optical lens of one embodiment has retainer feet forassembly purpose on the back. The feet are non-optical parts and may beof any shape.

The secondary optical lens may be used with a light source that isselected from single-chip LED, a multi-chip LED and a COB (chip onboard) module LED light source.

The secondary optical lens may provide the light distribution from itscurved outer surface 12 along the Y-Y section are as follows: The lightrays emitted from point O at the center of the light-emitting face ofthe multi-chip LED light source are refracted by the concave incidentface 11 onto the base face of curved surface 12. The base face of curvedsurface 12 distributes the incident light rays in an oblique manner andthe axis of the emergent light rays is OT, i.e. all emergent light beamsexit along the OT axis after light distribution. The angle between therefracting axis OT and the optical axis OZ is δ, and δ is between 30degrees and 70 degrees. For the marginal light rays emitted from point Qat the center of the chip light-emitting face and crossing the rightmostside of the base face of curved face 12, the angle between the emergentmarginal light rays and the optical axis OZ is α, and α is between −20degrees and −45 degrees.

The secondary optical lens may have a distribution of a single light rayby the base face of curved surface 12 along the Y-Y section is asfollows: A light ray OB emitted from point O at the center of thelight-emitting face of the multi-chip LED light source is refracted bythe concave incident race 11 onto paint C on the base face of the curvedsurface 12 and outputted as light ray CD after light distribution.Assuming that the angle between light ray OB and optical axis OZ is θ1and the angle between the emergent light ray CD and the optical axis OZis θ2, both θ2 and θ1 shall satisfy the following light distributionconditions:

${\theta\; 2} = {\tan^{- 1}\left\{ {{\left( \frac{{90{^\circ}} - {\theta\; 1}}{{90{^\circ}} + \delta} \right)\left\lbrack {{\tan(\delta)} - {\tan(\alpha)}} \right\rbrack} + {\tan(\alpha)}} \right\}}$

The secondary optical lens of a preferred embodiment has a lightdistribution principles on the base face of its curved surface 12 alongthe X-X section are as follows: The light rays emitted from point O atthe center of the light-emitting face of the multi-chip LED light sourceare refracted by the concave incident face 11 onto the base face ofcurved surface 12. The base face of curved surface 12 distributes theincident light rays in a wide-angle spectrum. The angle of emergentlight rays has a full width of 2Ψ, and 2Ψ is between 120 degrees and 155degrees.

The secondary optical lens may have a distribution of a single light rayby the base face of curved surface 12 along the X-X section is asfollows; A light ray OP emitted from point O at the center of thelight-emitting face of multi-chip LED light source is refracted by theconcave incident face 11 onto point Q on the base face of curved surface12 and outputted as light ray QR after light distribution. Assuming thatthe angle between light ray OP and optical axis OZ is ξ1 and the anglebetween the emergent light ray QR and the optical axis OZ is ξ2, both ξ2and ξ1 shall satisfy: the following light distribution conditions:

${\xi\; 2} = {\tan^{- 1}\left\lbrack {\frac{\xi\; 1}{90{^\circ}} \cdot {\tan(\psi)}} \right\rbrack}$

The secondary optical lens of an exemplary embodiment has light-mixingfacets or windows on its curved surface 12 that may take the form of asmall plane, a small convex face or a small concave face. The facetsgenerate a diffused light beam with a very small diffusion angle. Thediffused light beams generate a light-mixing effect after overlapping.The overlapped light patches have uniform color temperature.

The secondary optical lens may provide light-mixing of a single facet onits curved surface 12 along the Y-Y section is as follows; Assuming thatthe camber line of the section of a small facet on curved surface 12 isC1-C′-C2; that the camber line has a radius of curvature of R′; and thatcamber line C1-C-C2 of the base face of curved surface 12 at this pointhas a local radius of curvature of R, camber lines C1-C′-C2 and C1-C-C2will form a miniature false lens. The light ray emitted from point O atthe center of the LED light-emitting face will generate an angle ofdivergence at a size of ±Δθ here after passing this false lens. Theangle of divergence ±Δθ equals the numerical aperture angle of the falselens formed, and is related to the lamina's radius of curvature R′ andthe local radius of curvature R of the base face of curved surface 12 atthis point. For Δθ, a range of 3 degrees˜5 degrees is preferablyselected.

The secondary optical lens of an example uses light-mixing of a singlefacet on its curved surface 12 along the X-X section is as follows:Assuming that the camber line of the section of a small lamina attachedon curved surface 12 is Q1-Q′-Q2; that the camber line has a radius ofcurvature of R′ and that camber line Q1-Q-Q2 of the base face of curvedsurface 12 at this point has a local radius of curvature of R, camberlines Q1-Q′-Q2 and −Q1-Q-Q2 will form a miniature false lens. The lightrays emitted from point O at the center of the LED light-emitting facewill generate an angle of divergence at a size of ±Δξ here after passingthis false lens. The angle of divergence ±Δξ equals the numericalaperture angle of the false lens formed, and is related to the lamina'sradius of curvature R′ and the local radius of curvature R of the baseface of curved surface 12 at this point. For Δξ, a range of 3 degrees˜5degrees is preferably selected.

The secondary optical lens may have a micro-prism array with reflectiveeffects is designed at the bottom thereof. The abovementionedmicro-prism may have a pyramid, a corner cube or a conical structure.

Thus, there is provided a secondary optical technology of LED(light-emitting diode) road illumination, particularly a secondaryoptical lens characterized by light-mixing effect and uniform colortemperature, used for multi-chip LED light source. The structure of thesecondary optical lens is characterized in that: The lens consists ofthe external laminated curved surface for light distribution, theconcave incident face proximal to the LED side, the reflectivemicro-prism array face on the bottom, and the retainer feet for assemblypurpose. The optical characteristics of the external laminated curvedsurface for light distribution of the lens are as follows: Itdistributes the light rays emitted by LED within a wide-angle spectrumalong the X-X section and within a non-axisymmetric and oblique spectrumalong the Y-Y section. This curved surface for light distribution hasmany miniature facets or windows thereon for light-mixing effect. Alllight rays outputted from each miniature facet have a very smalldiffusion angle of their own, and they form light patches of uniformcolor temperature upon overlapping. This curved surface has an obliqueaxis along the Y-Y section, and forms an angle δ with the LED opticalaxis: δ is between 30 degrees and 70 degrees. The concave incident faceof the secondary optical lens is proximal to the LED side, and is usedto collect the light rays emitted by LED and refract them onto theexternal curved surface for light distribution. The reflectivemicro-prism array face on the bottom of the secondary optical lens isused to collect stray light scattered from the external curved surfacefor light distribution and output them again through the curved surfacefor light distribution, hence increasing the efficiency of the lens. Theretainer feet for assembly purpose of the secondary optical lens arenon-optical parts and may be of any shape. The light sources adopted forthe lens may include single-chip LED, multi-chip LED and COB module LEDlight source.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A lens for an LED street lamp for use with an LEDlight source having a primary lens, comprising: a lens body of asecondary optical lens, the lens body having: a curved outer surfacefrom which light is emitted, the curved outer surface having a firstperimeter portion and a second perimeter portion opposite the firstperimeter portion; a back surface opposite the curved outer surface, theback surface defining a recess for receiving the LED light source, therecess being closer to the first perimeter portion than to the secondperimeter portion; a reflective micro-prism array formed on the backsurface; the curved outer surface defining a concave surface portion atthe first perimeter portion; a plurality of facets on the curved outersurface; and a mounting structure for mounting the lens body, whereinthe lens body has a longitudinal axis and a transverse axis, the lensbody being shaped to provide optical characteristics to emit light fromthe LED light source over a wide distribution angle at a cross sectionalong the longitudinal axis and to emit light from the LED light sourceover an oblique distribution angle at a cross section along thetransverse axis.
 2. A lens as claimed in claim 1, wherein each of thefacets on the curved outer surface of the lens body is configured tooutput light over a narrow angle, the facets being arranged to emitlight patches that overlap light emitted from other facets to providelight mixing so that a substantially uniform color temperature light isoutput from the secondary lens.
 3. A lens as claimed in claim 1, whereinthe curved outer surface of the lens body is shaped to emit light at anaxis of refraction that is disposed at an angle relative to an opticalaxis of the light source of between 30 degrees and 70 degrees inclusiveat a cross section of the lens body along the transverse axis.
 4. A lensas claimed in claim 1, wherein the recess includes a surface facing theLED light source that is configured to collect light rays emitted by theLED light source and refract the light rays toward the external curvedsurface for light distribution.
 5. A lens as claimed in claim 1, whereinthe reflective micro-prism array on the back surface is configured tocollect light reflected internally by the curved outer surface and toreflect the collected light toward the curved outer surface todistribution by the lens body.
 6. A lens as claimed in claim 1, whereinthe mounting structure includes a plurality of retainer feet extendingfrom the back surface of the lens body, the retainer feet beingnon-optical elements.
 7. A lens as claimed in claim 1, wherein the lensbody is configured for use with at least one of the LED light sourcesselected from the group consisting of: a single chip LED light source, amulti-chip LED light source, and a chip-on-board module LED lightsource.
 8. A lens as claimed in claim 1, wherein the lens body is shapedto refract light from a center of the light source so that light emittedfrom the lens body is emitted with an axis of refraction that isdisposed at an angle of between 30 degrees and 70 degrees inclusive froman optical axis of the LED light source at a cross section along thetransverse axis of the lens body, the lens body being shaped to refractlight from a center of the light source so that a marginal emitted lightray is disposed at an angle of −20 degrees to −45 degrees inclusiverelative to the optical axis of the light source at a cross sectionalong the transverse axis of the lens.
 9. A lens as claimed in claim 1,wherein the lens body is shaped to refract a single ray of light emittedfrom a center of the light source at an angle θ1 relative to the opticalaxis of the light source so that the ray of light is emitted from thecurved outer surface at an angle of θ2 relative to the optical axis ofthe light source, wherein θ1 and θ2 satisfy the equation${{\theta\; 2} = {\tan^{- 1}\left\{ {{\left( \frac{{90{^\circ}} - {\theta\; 1}}{{90{^\circ}} + \delta} \right)\left\lbrack {{\tan(\delta)} - {\tan(\alpha)}} \right\rbrack} + {\tan(\alpha)}} \right\}}},$wherein δ is an angle of an axis of refraction relative to the opticalaxis of the light source and a is an angle of a marginal light rayrelative to the optical axis of the light source, at a cross sectionalong the transverse axis of the lens.
 10. A lens as claimed in claim 1,wherein the lens body is shaped to refract light from a center of thelight source so that the light emitted from the lens body is distributedin an emission angle of between 120 degrees to 155 degrees inclusive ata cross section along the longitudinal axis of the lens.
 11. A lens asclaimed in claim 1, wherein the lens body is shaped to refract a singleray of light emitted from a center of the light source at an angle ξ1relative to an optical axis of the light source so that the ray of lightis emitted from the curved outer surface at an angle ξ2 relative theoptical axis of the light source, wherein ξ1 and ξ2 satisfy the equation${{\xi\; 2} = {\tan^{- 1}\left\lbrack {\frac{\xi\; 1}{90{^\circ}} \cdot {\tan(\psi)}} \right\rbrack}},$wherein ψ is an angle of distribution of light from the lens body, at across section along the longitudinal axis of the lens.
 12. A lens asclaimed in claim 1, wherein the facets include at least one of a flatplane, a concave face, and a convex face, the facets being arranged toemit light patches that overlap light emitted from other facets toprovide light mixing so that a substantially uniform color temperaturelight is output from the secondary lens.
 13. A lens as claimed in claim1, wherein the surface of a facet on the curved outer surface and aprojection of the facet on the inner surface of the recess withreference to a center of the light source form a false lens having adivergent effect on light emitted from the facet, wherein light emittedfrom a center of the light source through the facet is spread by adivergent angle of approximately 3 degrees to 5 degrees inclusive, alonga cross section taken along a transverse axis of the lens.
 14. A lens asclaimed in claim 1, wherein the surface of a facet on the curved outersurface and a projection of the facet on the inner surface of the recesswith reference to a center of the light source form a false lens havinga divergent effect on light emitted from the facet, wherein lightemitted from a center of the light source through the facet is spread bya divergent angle of approximately 3 degrees to 5 degrees inclusive,along a cross section taken along a longitudinal axis of the lens.
 15. Alens as claimed in claim 1, wherein the micro-prism array on the backsurface of the lens body includes one of a pyramid reflector structure,a cube-corner reflector structure, and a conical reflector structure.16. A method for directing light from an LED light source onto asurface, the light source defining a parallel plane that is parallel toa light emitting surface of the LED light source, comprising: enclosinga light emitting portion of the LED light source with a first refractingsurface of an optical body, disposing the first refracting surface at asubstantially constant distance from the LED light source in a firstperpendicular plane; disposing the first refracting surface at a varyingdistance from the LED light source in a second perpendicular plane, thefirst and second perpendicular planes being perpendicular to one anotherand perpendicular to the parallel plane of the LED light source;directing light from the LED light source into the first refractingsurface of the optical body; emitting the light from the LED lightsource from a second refracting surface of the optical body, the emittedlight defining a refracting axis offset by an angle from the firstperpendicular plane, the refracting axis of the emitted light beingdisposed in the second perpendicular plane, the emitted light having agreatest intensity at the refracting axis; the emitted light includingemitting the light from the LED light source in an emission patternhaving a greater extent along an axis parallel to the firstperpendicular plane and a lesser extent along an axis in the secondperpendicular plane; reflecting a portion of the light from the LEDlight source at the second refracting surface to generate firstreflected light; and reflecting the first reflected light at areflecting surface to provide a second reflected light, the secondreflected light being directed toward the second refracting surface.